A mash up used to mean remixing two songs into something new and cool but now the term has been hijacked by geeks to means mixing two or more web-based data sources and/or services.

Paul Rademacher is the author of the Housing Maps mash-up which he used as a way to find a house using Craig'sList + Google Maps. The data obtained from Craig's List is fetched via screen scraping. Although Craig's List has RSS feeds, they didn't meet his needs. Paul also talked about some of the issues he had with building the site such as the fact that since most browsers block cross-site scripting using XMLHttpRequest then a server needs to be set up to aggregate the data instead of all the code running in the browser. The site has been very popular and has garnered over 900,000 unique visitors based solely on word-of-mouth.

The question was asked as to why he didn't make this a business but instead took a job at Google. He listed a number of very good reasons

He did not own the data that was powering the application.

The barrier to entry for such an application was low since there was no unique intellectual property or user interface design to his application

I asked whether he'd gotten any angry letters from the legal department at Craig's List and he said they seem to be tolerating him because he drives traffic to their site and caches a bunch of data on his servers so as not to hit their servers with a lot of traffic.

A related mash-up site which scrapes real estate websites called Trulia was then demoed. A member of the audience asked whether Paul thought the complexity of mash-ups using more than two data sources and/or services increased in a linear or exponential fashion. Paul said he felt it increased in a linear fashion. This segued into a demo of SimplyHired with integrates with a number of sites including PayScale, LinkedIn, Job databases, etc.

At this point I asked whether they would have service providers giving their perspective on making money from mash-ups since they are the gating factor because they own the data and/or services mash-ups are built on. The reply was that the eBay & Yahoo folks would give their perspective later.

Then we get a demo of a Google Maps & eBay Motors mash-up. Unlike the Housing Maps mash-up, all the data is queried live instead of cached on the server. eBay has dozens of APis that encourage people to build against their platform and they have an affiliates program so people can make money from building on their API. We also got showed Unwired Buyer which is a site that enables you to bid on eBay using your cell phone and even calls you just before an auction is about to close. Adam Trachtenberg pointed out that since there is a Skype API perhaps some enterprising soul could mash-up eBay & Skype.

Jeffrey McManus of Yahoo! pointed out that you don't even need coding skills to build a Yahoo! Maps mash-up since all it takes is specifying your RSS feed with longitude and latitude elements on each item to have it embedded in the map. I asked why unlike Google Maps and MSN Virtual Earth, Yahoo! Maps doesn't allow users to host the maps on their page nor does there seem to be an avenue for revenue sharing with mash-up authors via syndicated advertising. The response I got was that they polled various developers and there wasn't significant interest in embedding the maps on developer's sites especially when this would require paying for hosting.

The following items were then listed as the critical components of mash-ups - AJAX (Jeffrey McManus said it isn't key but a few of the guys on the panel felt that at least dynamic UIs are better) - APIs - Advertising - Payment - Identity/Acct mgmt - Mapping Services - Content Hosting - Other?

On the topic of identity and account management, the problem of how mash-ups handle user passwords came up as a problem. If a website is password protected then user's often have to enter their usernames and passwords into third party sites. An example of this was the fact that PayPal used to store lots of username/password information of eBay users which caused the company some consternation since eBay went through a lot of trouble to protect their sensitive data only to have a lot of it being stored on Paypal servers.

eBay's current solution is similar to that used by Microsoft Passport in that applications are expected to have user's login via the eBay website then the user is redirected to the originating website with a ticket indicating they have been authenticated. I pointed out that although this works fine for websites, it offers no solution for people trying to build desktop applications that are not browser based. The response I got indicated that eBay hasn't solved this problem.

My main comment about this panel is that it didn't meet expectations. I'd expected to hear a discussion about turning mashups [and maybe the web platforms they are built on] into money making businesses. What I got was a show-and-tell of various mapping mashups. Disappointing.